A method of obtaining a nitride bulk single crystal by recrystallizing from supercritical ammonia-containing solution is disclosed in Japanese Patent Application No. 2002-143449. The apparatus for obtaining a nitride bulk single crystal using supercritical ammonia-containing solution comprises an autoclave for preparing supercritical solvent equipped with a convection control means for establishing a convection flow, and mounted inside a furnace unit equipped with a heating device and a cooling device,
wherein the furnace unit is controlled to have a predetermined temperature gradient within the autoclave by the heating device and/or cooling device,
wherein the convection control means for establishing convection flow comprises at least one horizontal baffle having a central opening and/or a space between the baffle and an inner wall of the autoclave, and separating the dissolution zone where a feedstock is located above the baffle from the crystallization zone where a seed is located below the baffle.
Furthermore, it is found that a convection flow rate of the supercritical solution between the dissolution zone and the crystallization zone may be determined by a degree of opening of the convection control means and a temperature difference between the dissolution zone and crystallization zone etc.
The result of the inventors' research shows that a growth rate of 10 μm/h or more is required for commercially manufacturing of nitride. It is also found to be necessary that nitride is dissolved in the supercritical solvent containing ammonia and at least alkali metal ions to make the supercritical solution, in which the nitride has a negative temperature coefficient of solubility and the supercritical solution is supplied from the dissolution zone to the crystallization zone where a seed is located through the convection control means so that nitride crystal can be selectively grown on the seed arranged in the autoclave by maintaining supersaturation of the supercritical solution with respect to the seed at the predetermined raised temperature and controlling below a certain concentration so as not to allow spontaneous crystallization.